Project Summary/Abstract Histone deacetylases (HDACs) are a group of epigenetic enzymes that are important in regulating gene transcription and other cellular processes. HDAC1 is implicated in various developmental program, including hematopoiesis. We and others previously showed that HDAC1 is an important regulator for GATA-1 function in FOG-1 dependent manner. During erythroid differentiation, HDAC1 within FOG-1 associated NuRD complex is acetylated and becomes inactive. Inactivated HDAC1 converts the NuRD into a coactivator complex to activate GATA-1 dependent gene transcription. Here we show that GATA-1 can also associate with HDAC1 in a FOG-1 independent manner, importantly, this association is required for GATA-1 deacetylation, therefore suggesting another layer of regulation for GATA-1 function. The significance of these findings is demonstrated by our observation that mutations in GATA-1 that disrupt HDAC1 interactions (GATA-1 2RA mutants) cause erythroid differentiation defects in mice. The central hypothesis for this proposal is that GATA-1 and HDAC1 interaction as well as acetylation of GATA-1 regulates the erythroid differentiation program and erythroid enhancer/promoter chromatin structure during erythropoiesis. In this proposal, we will investigate the mechanism underlying the regulation of GATA-1 activity by HDAC1 in a FOG-1 independent manner and to study the importance of direct HDAC1 binding in GATA-1 mediated gene transcription program and global GATA-1 recruitment and chromatin accessibility. Finally we propose to study the role of HDAC1 in regulating erythroid lineage differentiation by direct interacting with GATA-1 in a mouse model. By completion of this proposal, we will be able to gain insight into the function of dynamic GATA-1 acetylation/deacetylation and the importance of GATA-1/HDAC1 direct interactions. We will also learn the differential requirement of FOG-1 dependent and independent HDAC1 recruitment for erythropoiesis. The Knock in mouse work will further enable us to delineate the requirement of GATA-1/HDAC1 interactions for lineage specific development. Thus, this study will lead to in depth understanding of GATA-1 function in erythropoiesis and beyond.